Recent advances of the wireless communication technology lead to the coexistence of systems using different communication schemes. For example, systems using the 2G Code Division Multiple Access (CDMA) scheme coexist with systems using the 3G International Mobile Telecommunication (IMT)-2000 scheme and systems using the 4G Orthogonal Frequency Division Multiplexing (OFDMA) scheme. The systems using different communication schemes provide services using different frequency bands.
Limited frequency resources for radio communications are insufficient for the coexisting systems of the different communication schemes.
To address this problem, research has been conducted on a Cognitive Radio (CR) technique, which senses unused frequency band or channel from the frequency bands allocated to a specific system and allows other system to use the sensed frequency band or channel. For instance, when a system for transmitting an incumbent signal allocates the frequency bands, the system does not use some channels of the allocated frequency band. In this case, to transmit the incumbent signal, a wireless communication system using the CR function detects the unused channels in the allocated frequency band and uses the detected channels to provide service to terminals in the service coverage.
When using the CR function as above, the wireless communication system services the terminals in the service coverage using the unused channels in the frequency band allocated to the particular system. When the incumbent signal intends to use the operating channels in use, the cells using the CR function should empty their operating channels. Accordingly, with the CR function, the wireless communication system cannot deliberately conduct the frequency planning in advance.
When using the CR function, the cells constitute a set of candidate channels to change their operation channel in use. When the incumbent signal intends to use the operating channel, the cells change the operating channel by selecting one of the candidate channels of the candidate channel set.
When the channel selected by the cell of the CR function to change the operating channel is the same as a channel of a neighbor cell, the wireless communication system is subject to the degradation of the system performance because of interference from the neighbor cell.
Hence, the wireless communication system using the CR function needs a basis for the cells to select channels to be included to the candidate channels and a basis for the cells to select a channel from the candidate channel set.